Orthopedic bone cement is used in many surgical procedures throughout the world to secure hip, knee and other metallic prostheses in an appropriate anatomical position. Orthopedic bone cement is also used in procedures such as vertebroplasty, which is used to treat osteoporosis, a condition which causes progressive bone loss, creating structural weakness and skeletal fragility in hundreds of thousands of people throughout the world every year. The vertebroplasty procedure involves the injection of bone cement via a needle or syringe into a vertebral body of a patient, thereby stabilising, strengthening and reinforcing the bone and alleviating chronic back pain and preventing further vertebral damage.
Conventionally, a number of different types of bone cement may be used in a powder/liquid form; the three main types used for vertebroplasty, for example, being calcium sulphate, calcium phosphate and variations of polymethylmethacrylate (PMMA). Special formulations of PMMA have also been developed that may include, for example, the addition of barium, (e.g. for use in X-ray) and the addition of hydroxyapetite (e.g. to promote bone growth).
Since different types of bone cement are used in different procedures, and since these different types of bone cement may have different physical properties, (e.g. viscosity), the apparatus and method by which the bone cement is prepared also varies.
UK Patent No. GB 2 276 560 describes a bone cement mixing device comprising a mixing bowl with a lid having a handle extending outwardly therefrom. A mixing paddle comprising a shaft and vanes extending outwardly therefrom extends into the bowl from the lid. A step up gear mechanism is provided between the paddle and the lid such that, as the handle rotates, the paddle also rotates. The drive wheel of the gear mechanism is also caused to rotate and drives the driven wheel which causes the shaft of the paddle to rotate about its own axis as the paddle moves around the bowl.
WO 95/22402 describes a device for mixing and delivering bone cement comprising a mixing chamber, a mixing element and drive means for causing rotation of the mixing element. The drive means may be a handle axially movable relative to the mixing chamber so that a gear mechanism between the handle and the mixing element translates axial movement of the handle into rotation of the mixing element. The device may be used in conjunction with a syringe so that the cylinder of the syringe forms the body of the mixing chamber and a plunger is slidably mounted at one end of the cylinder for causing ejection of the mixed cement.
U.S. Pat. No. 5,876,116 describes an integrated bone cement mixing and discharging apparatus for use in surgical procedures for affixing prostheses to a bone or joint structure for improving the strength, rigidity and movement of the bone/joint structure. The apparatus is used for mixing the bone cement components and delivering the mixed bone cement to a desired location. The apparatus comprises a mixing chamber that is integrally combined with a delivery chamber or tube that has one end incorporating a cement delivering outlet port. The two chambers are movable between two alternate positions, a first position wherein each chamber is sealed from the other and a second position wherein the two chambers are in direct communication with each other. The mixing chamber is therefore operated independently of the delivery chamber for preparing the bone cement and once prepared, transferred from the mixing chamber through the delivery chamber or tube for immediate use.
Conventionally, for vertebroplasty, the bone cement is prepared immediately prior to each procedure by manually mixing a powder and a liquid in a bowl using a spatula or the like, and then transferring the mixed bone cement into a syringe or delivery gun for application.
One conventional method for performing vertebroplasty using a low viscosity bone cement such as PMMA involves mixing a powder and liquid in an open bowl with a spatula, then pouring, scraping or aspirating the mixture into a syringe for injection by hand into a collapsing vertebral body. In this way, the bone cement can stabilise and strengthen the bone, thereby alleviating chronic back pain and preventing further vertebral damage by reinforcing the fractured bone.
An alternative method of performing vertebroplasty comprises mixing the components in a shaker and then aspirating, via a connector, into either a 10 ml syringe or a 220 ml syringe, which is then used to fill syringes of various sizes. Following the filling of the syringes, a biopsy needle or a biopsy needle with a catheter may be connected to the syringe and the bone cement mixture injected into the vertebra of the patient.
A further method for performing vertebroplasty involves mixing the liquid and powder in a shaker or in an open bowl with a spatula (as before), aspirating or pouring the mixture into a 10 ml syringe that is used with a delivery gun, then connecting a biopsy needle or a biopsy needle with a catheter to the syringe and injecting the bone cement mixture into the vertebra of the patient.
Thus, although conventionally the mixing of bone cement may be achieved using a number of different apparatus and methods, there is no apparatus available that allows for the quick, simple and effective mixing and discharging of bone cement directly into a variety or plurality of syringes.
In general, the manual transfer of mixed bone cement from the mixing bowl or shaker to the syringes is a messy and time-consuming process. These methods also have further disadvantages in that fumes produced during the mixing of the bone cement may be a problem for operators both within the orthopedic and radiology fields.
A first aspect of the present invention provides an apparatus for mixing and discharging bone cement compounds comprising a first end and a second end, with a longitudinal axis extending between the first end and the second end, a mixing region, at least one exit port, and valve means for preventing or enabling communication between the mixing region and at least one exit port, wherein the at least one exit port is located between said first end and said second end and wherein said valve is moveable along said longitudinal axis between a first position in which the valve prevents communication between the mixing region and the at least one exit port and a second position wherein the valve enables communication between the mixing region and the at least one exit port.
Although syringes to be filled could be attached directly to the exit port(s), in a preferred embodiment, connection means are provided on the exit port(s) for the connection of syringes. These connection means may comprise valves for preventing or enabling flow through the connection means from the exit port(s) to the syringe(s). Alternatively, the exit ports may be blocked via the use of stoppers which fit into the exit ports. The connection means may be provided in different sizes or in the form of an adaptor for different sized syringes.
Since the apparatus of the present invention may be used in conjunction with a plurality of different sized adaptors, it is possible to fill a wide range of different sized syringes using the same apparatus. Additionally, since the apparatus of the present invention may comprise more than one exit port, a plurality of syringes (either the same size or different sizes) may be filled at the same time, from the same batch of mixed bone cement.
Whilst the user may be able to judge when the valve is in the open or closed position, in a preferred embodiment, the apparatus of the present invention comprises means for locating the valve in the first position and/or means for locating the valve in the second position.
In a preferred embodiment, the apparatus of the present invention also comprises means for preventing the valve from being accidentally removed from the second end of the apparatus. In one embodiment, this means comprises at least one end-stop that is provided on the exterior surface of the valve and which abuts an opposing surface, such as a ledge, that is provided on the interior surface of the apparatus.
The apparatus of the present invention may further comprise a base, which allows the apparatus to be freestanding and so increasing ease of use. Due to the fact that the exit port(s) are provided between the first and second ends, the base may be provided at the second end of the apparatus. The base may therefore act as a support on which the apparatus stands and may be integral with or attachable to the apparatus and/or the valve. The base may also be associated with the valve, so that movement of the base causes movement of the valve. In a preferred embodiment, rotation of the base causes longitudinal or axial movement of the valve. This thereby aids manipulation of the valve within the apparatus and provides a simple means for moving the valve along the longitudinal axis of the apparatus.
It is possible to provide more than one exit port between the first end and the second end, thereby allowing for the connection of a plurality of syringes so that the operator may fill more than one syringe at a time. In this way, the present invention achieves easier transfer of mixed cement to more discharging syringes or the like, with the minimum of time, mess and effort.
Thus, the present invention provides a relatively simple, low cost and effective apparatus for mixing and discharging bone cement into a syringe(s), whilst also providing an improved mixing action and producing minimal fumes.